I consider silverlight just broken.
The toggle for gpu acceleration in the silverlight gui doesnt do anything, so its generally left on.
with gpu acceleration on the gpu (at leats my gpu) saturates and cant handle sky go. It runs at about 5fps at full screen, thanfully sky allow to go to software mode and in that mode it uses about 3% cpu with no issues.
All other sites dont supply a toggle tho and gpu is forced on, on netfdlix if I use the latest version of silverlight I cant get smooth performance full screen, I have to use an old insecure version. BT sport plays ok but that uses a very low bitrate so may be something to do with it.
So to me the issues are a broken gpu implentation and broken gpu on/off toggle. But these content providers need to get away from silverlight as microsoft have ditched it themselves. So they using a dead platform now to deliver their content. As it seems DRM is of upmost importance above all else. But this breakthrough it seems some kind of DRM extensions have been developed for html5 which is why they now have it working on IE11.
BT Infinity 2 Since Dec 2012 - BQM